This invention relates to a radioactive ray gauge suitable for measuring the thickness of metal coatings or the thickness of paint on ON-Line systems.
The radioactive ray gauges have come into use in recent years for measuring continuously the thickness of metal coatings. This measuring process comprises steps of providing a primary radioactive ray (excited X-ray) to the surface of steel sheet after coating, measuring the intensity of a secondary radioactive ray (fluorescent X-ray) and detecting continuously the metal coating with the measured intensity.
However, it is disadvantageous that the conventional measuring head (which carries the radioactive ray detector) produces fluctuating errors of the measured value due to any one or some combination of the phenomenon: thickness variation of the advancing sheet to be measured; bending or warping of the sheet; and which pass line flutter produces the variation of the dynamic distance between the sheet and the measuring head since the conventional measuring head is fixed apart from the advancing sheet.
Accordingly, conventionally, by improving the collimeter or the like disposed in the measuring head, the error in the measurement caused by the variation of the distance between the sheet and the measuring head can be reduced to a more acceptable range.
However, in this system, it is difficult from the technical point to obtain enough compensated characteristic in case the variation of the distance between the sheet and the measuring head is too large.
Besides, the intensity of the secondary radioactive ray which is detected by the measuring head decreases when the above improvement is made.
In the radioactive ray gauge in the ON-Line system, it is necessary that the intensity of the secondary radioactive ray to be obtained as the input signal is as great as possible so that the measuring time is reduced and the intensity of the secondary ray exists in the required statistical variation error range.
At this point, too, it is difficult that the above problems are dissolved since the intensity of the secondary radioactive ray measured in the aforementioned improvement of the characteristic also becomes lower.
Needless to say, the intensity of the secondary radioactiver ray is increased if the intensity of the primary radioactive ray increases.
However, this increase is not desired from the safety point of view. Therefore, it is an object of the invention to provide a radioactive ray gauge for making precise measurement, and eliminating the effect depending on the dynamic variation of the distance between the sheet surface and the measuring head caused by sheet thickness variation, sheet bending, fluttering or the like, on the ON-Line system, provided with the correcting mechanism which corrects the relative position of the measuring head to the sheet surface in response to-and-fro movement of the sheet surface against the head.